Add debugs logs on access to external IDs and group names note branches

We want to see in a trace when a request triggers many accesses to the
external IDs or group names note branches.

Change-Id: Ia05ad6458b0203a340bde76ae4c256cb8e800d1b
Signed-off-by: Edwin Kempin <ekempin@google.com>

java/com/google/gerrit/server/account/externalids/ExternalIdNotes.java

@@ -615,6 +615,8 @@ public class ExternalIdNotes extends VersionedMetaData {
 
   @Override
   protected void onLoad() throws IOException, ConfigInvalidException {
+    logger.atFine().log("Reading external IDs");
+
     noteMap = revision != null ? NoteMap.read(reader, revision) : NoteMap.newEmptyMap();
 
     if (afterReadRevision != null) {
@@ -701,6 +703,8 @@ public class ExternalIdNotes extends VersionedMetaData {
       return false;
     }
 
+    logger.atFine().log("Updating external IDs");
+
     if (Strings.isNullOrEmpty(commit.getMessage())) {
       commit.setMessage("Update external IDs\n");
     }